In searching for oil, gas and other underground deposits of minerals, exploratory holes are drilled and core samples are taken so that an evaluation may be made of the geological, mineralogical and physical properties and characteristics of the strata of interest. Information is obtained from these samples as to, for example, porosity, permeability, fluid content, grain size, compressibility, acoustical qualities, mineral composition and acid solubility.
In order to obtain an accurate evaluation of the properties and characteristics of the strata of interest, the sample is preferably taken over a substantial length of the bore hole. There are two types of coring procedures, the first is drilling and retrieving the bore in a central core, the core being substantially the size of the hole itself, and second, retrieving a sample from the sidewall of the bore hole. In the central coring method, the core is formed simultaneous with the drilling of the bore hole which restricts the core sample to the bottom of the bore hole. Therefore, the string must be lifted up at predetermined times during the drilling operation and the coring mechanism lowered into the hole.
In sidewall coring operation, a wireline system is typically utilized to lower the coring device down into the hole and then retrieve the samples. In one type of coring device, U.S. Pat. No. 3,405,772, issued to J. D. Wisenbaker et al. on Oct. 15, 1968, discloses a method for retrieving a triangular core sample. This device is lowered into the hole by wireline and then held against the walls of the bore hole at a predetermined distance therein. Two saw blades are then pushed outward against the sidewall to cut a triangular shaped core as the tool is pulled upward. A rotating canister is provided with a plurality of tubes, each containing a ten foot section of core. An electric motor is provided which is powered through the wireline to drive the saw blades.
A similar type of system is also illustrated in U.S. Pat. No. 3,173,500, issued to R. W. Stewart et al. on Mar. 16, 1965, and U.S. Pat. No. 3,430,716, issued to H. J. Urbanosky on Mar. 4, 1969.
In view of the above disadvantages with conventional coring and sidewall coring, there exists a need for a sidewall coring system that provides the ability to extract a continuous small strip of the sidewall or multiple intervals thereof without requiring the use of a wireline system or external power.